With the advent of the very deep submicron (VDSM) technologies, the process variations become more and more serious, and thus achieving high yield rates on semiconductor chips will be more difficult. In order to reduce the burden of manufacturers to maintain the manufacturability and high yield rates, a new design methodology, design for manufacturability (DFM), is suggested. This design methodology proposes that in order to improve the manufacturability and yield of a design, the manufacturability issues could be considered during the physical design stage.
In an IC layout, a via provides a connection between two net segments from adjacent metal layers. Due to the growing of the design scale and/or the jumper-based solution to avoid the antenna effect, the number of vias could become very large. However, due to various reasons such as cut misalignment in a manufacturing process, electromigration and thermal stress, a via may fail partially or completely. For a partially failed via, the contact resistance and the parasitic capacitance will increase and may induce timing problems. On the other hand, a complete via failure will leave an open net on the circuit. These may heavily impact on the functionality and yield of a design. Therefore, reducing the yield loss due to via failure is important in DFM.
A well known and highly recommended method to improve via yield is to add a redundant via adjacent to a single via, enabling a single via failure to be tolerated and also reducing the via resistance. Therefore, redundant vias do not hurt timing performance, and the reliability of a design can be improved.